1. Field of the Invention
The present invention is directed to printed circuit boards (PCBs) incorporating electro-optic modules such as optical transceivers and serial and parallel optics devices (collectively referred to as "optics devices") which have an optical connection to an off-PCB device or cable and electrical connections to the PCB.
2. The Background Art
Electro-optical devices are devices which include an optical input/output (I/O) interface and an electrical I/O interface. Common examples include optical transceivers which are attached to a printed circuit board (PCB) to receive/transmit electrical signals and have a connector for receiving a fiber optic cable.
Common PCB fabrication today uses surface mount technology (SMT). In SMT conductive pads are placed on a surface of a PCB, solder paste is screened onto the pads, and a pick and place machine places all of the SMT components in their respective correct places on the PCB with the leads of the SMT components in contact with the solder paste (which is usually slightly adhesive) on the pads of the PCB. The PCB assembly is then placed in a solder reflow oven which heats the PCB and components to a temperature where the solder paste reflows forming permanent electrical connections between the leads of the components and the pads of the PCB.
It is then necessary to remove the excess solder paste which contains corrosive flux materials to prevent corrosion of the PCB assembly over time. This process is usually carried out by immersion of the PCB assembly in a liquid solder flux removal agent which is usually water-based.
Unfortunately, optics devices, such as optical transceivers, are not entirely sealed due to the need to be able to connect optical fiber to the interior of the device. Such devices contain optical components and optical surfaces which do not respond well to high heat or a liquid phase cleaning process. Materials can be left behind, disrupting optical paths. Furthermore, because these devices usually include low temperature materials such as silicones, the high temperature processing of such optics devices is inadvisable and may lead to low yields and/or subsequent failure over time. Thus, such optics devices should not be exposed to elevated temperatures and excessive moisture.
It is possible to solder such components individually to a PCB using a known hot bar solder approach, but this apparatus is costly and time consuming. It also suffers from poor yield and can result in damage to the optics devices which are often relatively expensive devices.
A solder-type connection is also inadvisable for components with a high density of connections where the component is to be attached to a cable or like device. Where a cable is attached, it is almost inevitable that stress such as shear stresses will be imparted by the cable and its movement (or the attachment of a cable connector to a corresponding socket on the component) to the solder joints connecting the component to the PCB. Such stresses can cause cracks to develop in the connections over time and thereby cause intermittent and permanent failure of the PCB assembly.
Due to the high connection densities used in the types of PCB assemblies incorporating such electro-optic modules, it is extremely inadvisable to utilize techniques that are likely to require rework as rework attempts may cause difficult-to-detect collateral damage to the solder joints of surrounding components.
It would, therefore, be highly desirable to find a way to combine such optics devices with SMT PCBs without the need for soldering or exposure of the optics devices to elevated temperatures or moisture.